Method and apparatus for tuning a resistance and reactance of a wireless power transmitter testing unit

ABSTRACT

An apparatus for testing an impedance range of a wireless power transmitter is provided. The apparatus comprises an adjustable impedance circuit configurable to be connected to a power source. The apparatus further comprises a transformer coupled the adjustable impedance circuit. The apparatus further comprises a sensing circuit configured to sense a parameter indicative of a parasitic impedance of the adjustable impedance circuit. The apparatus further comprises a driver circuit configured to drive the transformer with a signal based on the sensed parameter that causes the transformer to apply a first voltage to the adjustable impedance circuit. The first voltage has a substantially same amplitude as a voltage drop caused by the parasitic impedance. The second voltage is out of phase with the voltage drop. The sensed parameter is a current circulating in the adjustable impedance circuit or a voltage across at least a portion of the adjustable impedance circuit.

FIELD

This application is generally related to testing of wireless powertransmitters, and more specifically to methods and apparatuses fortuning a resistance and/or reactance of a wireless power transmittertesting unit.

BACKGROUND

Wireless power transmitters are configured to operate within specifiedparameters under a range of loading conditions. In order to ensure thatthe wireless power transmitters operate within the specified parameters,testing equipment may subject the transmitters to a plurality of loadingconditions including various load impedances. To ensure the testingequipment is accurately recreating the desired load impedances, methodsand apparatuses for tuning a resistance and reactance of a wirelesspower transmitter testing unit are desirable.

SUMMARY

According to some implementations, an apparatus for testing an impedancerange of a wireless power transmitter is provided. The apparatuscomprises an adjustable impedance circuit configurable to be connectedto a power source. The apparatus comprises a transformer coupled to theadjustable impedance circuit. The apparatus comprises a sensing circuitconfigured to sense a parameter indicative of a parasitic impedance ofthe adjustable impedance circuit. The apparatus comprises a drivercircuit configured to drive the transformer with a signal based on thesensed parameter that causes the transformer to apply a first voltage tothe adjustable impedance circuit. The first voltage has a substantiallysame amplitude as a voltage drop caused by the parasitic impedance. Thefirst voltage is out of phase with the voltage drop.

In some other implementations, a method for testing an impedance rangeof a wireless power transmitter is provided. The method comprisessensing a parameter indicative of a parasitic impedance of an adjustableimpedance circuit configurable to be connected to a power source. Themethod further comprises driving a transformer coupled to the adjustableimpedance circuit with a signal based on the sensed parameter thatcauses the transformer to apply a first voltage to the adjustableimpedance circuit. The first voltage has a substantially same amplitudeas a voltage drop caused by the parasitic impedance. The first voltageis out of phase with the voltage drop.

In yet other implementations, an apparatus for testing an impedancerange of a wireless power transmitter is provided. The apparatuscomprises means for providing an adjustable impedance to a power source.The apparatus comprises means for sensing a parameter indicative of aparasitic impedance of the means for providing the adjustable impedance.The apparatus comprises means for applying a first voltage to the meansfor providing the adjustable impedance based on the sensed parameter.The first voltage has a substantially same amplitude as a voltage dropcaused by the parasitic impedance. The first voltage is out of phasewith the voltage drop.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects, as well as other features, aspects, andadvantages of the present technology will now be described in connectionwith various implementations, with reference to the accompanyingdrawings. The illustrated implementations, however, are merely examplesand are not intended to be limiting. Throughout the drawings, similarsymbols typically identify similar components, unless context dictatesotherwise. Note that the relative dimensions of the following figuresmay not be drawn to scale.

FIG. 1 is a functional block diagram of a wireless power transfersystem, in accordance with some exemplary implementations.

FIG. 2 is a functional block diagram of a wireless power transfersystem, in accordance with some other exemplary implementations.

FIG. 3 is a schematic diagram of a portion of transmit circuitry orreceive circuitry of FIG. 2 including a transmit or receive coupler, inaccordance with some exemplary implementations.

FIG. 4 shows a hybrid schematic/functional block diagram of an apparatusfor testing an impedance range of a wireless power transmitter, inaccordance with some exemplary implementations.

FIG. 5 shows another functional block diagram of an apparatus fortesting an impedance range of a wireless power transmitter, inaccordance with some other exemplary implementations.

FIG. 6 is a flowchart depicting a method for testing an impedance rangeof a wireless power transmitter, in accordance with some exemplaryimplementations.

FIG. 7 is a functional block diagram of an apparatus for testing animpedance range of a wireless power transmitter, in accordance with someother exemplary implementations.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the present disclosure. Theillustrative implementations described in the detailed description,drawings, and claims are not meant to be limiting. Other implementationsmay be utilized, and other changes may be made, without departing fromthe spirit or scope of the subject matter presented here. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein, and illustrated in the Figures, can bearranged, substituted, combined, and designed in a wide variety ofdifferent configurations, all of which are explicitly contemplated andform part of this disclosure.

Wireless power transfer may refer to transferring any form of energyassociated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield or an electromagnetic field) may be received, captured, or coupledby a “receive coupler” to achieve power transfer.

The terminology used herein is for the purpose of describing particularimplementations only and is not intended to be limiting on thedisclosure. It will be understood that if a specific number of a claimelement is intended, such intent will be explicitly recited in theclaim, and in the absence of such recitation, no such intent is present.For example, as used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items. It willbe further understood that the terms “comprises,” “comprising,”“includes,” and “including,” when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Expressions such as “at least oneof,” when preceding a list of elements, modify the entire list ofelements and do not modify the individual elements of the list.

FIG. 1 is a functional block diagram of a wireless power transfer system100, in accordance with some exemplary implementations. Input power 102may be provided to a transmitter 104 from a power source (not shown) togenerate a wireless (e.g., magnetic or electromagnetic) field 105 via atransmit coupler 114 for performing energy transfer. The receiver 108may receive power when the receiver 108 is located in the wireless field105 produced by the transmitter 104. The wireless field 105 correspondsto a region where energy output by the transmitter 104 may be capturedby the receiver 108. A receiver 108 may couple to the wireless field 105and generate output power 110 for storing or consumption by a device(not shown in this figure) coupled to the output power 110. Both thetransmitter 104 and the receiver 108 are separated by a distance 112.

In one example implementation, power is transferred inductively via atime-varying magnetic field generated by the transmit coupler 114. Thetransmitter 104 and the receiver 108 may further be configured accordingto a mutual resonant relationship. When the resonant frequency of thereceiver 108 and the resonant frequency of the transmitter 104 aresubstantially the same or very close, transmission losses between thetransmitter 104 and the receiver 108 are minimal. However, even whenresonance between the transmitter 104 and receiver 108 are not matched,energy may be transferred, although the efficiency may be reduced. Forexample, the efficiency may be less when resonance is not matched.Transfer of energy occurs by coupling energy from the wireless field 105of the transmit coupler 114 to the receive coupler 118, residing in thevicinity of the wireless field 105, rather than propagating the energyfrom the transmit coupler 114 into free space. Resonant inductivecoupling techniques may thus allow for improved efficiency and powertransfer over various distances and with a variety of inductive couplerconfigurations.

In some implementations, the wireless field 105 corresponds to the“near-field” of the transmitter 104. The near-field may correspond to aregion in which there are strong reactive fields resulting from thecurrents and charges in the transmit coupler 114 that minimally radiatepower away from the transmit coupler 114. The near-field may correspondto a region that is within about one wavelength (or a fraction thereof)of the transmit coupler 114. Efficient energy transfer may occur bycoupling a large portion of the energy in the wireless field 105 to thereceive coupler 118 rather than propagating most of the energy in anelectromagnetic wave to the far field. When positioned within thewireless field 105, a “coupling mode” may be developed between thetransmit coupler 114 and the receive coupler 118.

FIG. 2 is a functional block diagram of a wireless power transfer system200, in accordance with some other exemplary implementations. The system200 may be a wireless power transfer system of similar operation andfunctionality as the system 100 of FIG. 1. However, the system 200provides additional details regarding the components of the wirelesspower transfer system 200 as compared to FIG. 1. The system 200 includesa transmitter 204 and a receiver 208. The transmitter 204 includestransmit circuitry 206 that includes an oscillator 222, a driver circuit224, and a filter and matching circuit 226. The oscillator 222 may beconfigured to generate a signal at a desired frequency that may beadjusted in response to a frequency control signal 223. The oscillator222 provides the oscillator signal to the driver circuit 224. The drivercircuit 224 may be configured to drive the transmit coupler 214 at aresonant frequency of the transmit coupler 214 based on an input voltagesignal (V_(D)) 225.

The filter and matching circuit 226 filters out harmonics or otherunwanted frequencies and matches the impedance of the transmit circuitry206 to the transmit coupler 214. As a result of driving the transmitcoupler 214, the transmit coupler 214 generates a wireless field 205 towirelessly output power at a level sufficient for charging a battery236.

The receiver 208 comprises receive circuitry 210 that includes amatching circuit 232 and a rectifier circuit 234. The matching circuit232 may match the impedance of the receive circuitry 210 to theimpedance of the receive coupler 218. The rectifier circuit 234 maygenerate a direct current (DC) power output from an alternate current(AC) power input to charge the battery 236. The receiver 208 and thetransmitter 204 may additionally communicate on a separate communicationchannel 219 (e.g., Bluetooth, Zigbee, cellular, etc.). The receiver 208and the transmitter 204 may alternatively communicate via in-bandsignaling using characteristics of the wireless field 205. In someimplementations, the receiver 208 may be configured to determine whetheran amount of power transmitted by the transmitter 204 and received bythe receiver 208 is appropriate for charging the battery 236.

FIG. 3 is a schematic diagram of a portion of the transmit circuitry 206or the receive circuitry 210 of FIG. 2, in accordance with someexemplary implementations. As illustrated in FIG. 3, transmit or receivecircuitry 350 may include a coupler 352. The coupler 352 may also bereferred to or be configured as a “conductor loop”, a coil, an inductor,or a “magnetic” coupler. The term “coupler” generally refers to acomponent that may wirelessly output or receive energy for coupling toanother “coupler.”

The resonant frequency of the loop or magnetic couplers is based on theinductance and capacitance of the loop or magnetic coupler. Inductancemay be simply the inductance created by the coupler 352, whereas,capacitance may be added via a capacitor (or the self-capacitance of thecoupler 352) to create a resonant structure at a desired resonantfrequency. As a non-limiting example, a capacitor 354 and a capacitor356 may be added to the transmit or receive circuitry 350 to create aresonant circuit that selects a signal 358 at a resonant frequency. Forlarger sized couplers using large diameter couplers exhibiting largerinductance, the value of capacitance needed to produce resonance may belower. Furthermore, as the size of the coupler increases, couplingefficiency may increase. This is mainly true if the size of bothtransmit and receive couplers increase. For transmit couplers, thesignal 358, with a frequency that substantially corresponds to theresonant frequency of the coupler 352, may be an input to the coupler352.

In order to ensure that the wireless power transmitters, such as thetransmitter 204, operate within the specified parameters, testingequipment may subject the transmitter 204 (e.g., at the output of thefilter and matching circuit 226) to a plurality of loading conditionshaving various load impedances. However, in practice, parasiticimpedances (e.g., a parasitic capacitance) between electrical componentsin such testing equipment may prevent the testing equipment fromaccurately presenting very low impedances to the wireless powertransmitter 204 under test. For example, in some cases tuning suchtesting equipment for a desired impedance of 1.2Ω, for example, maycause the testing equipment to provide an actual impedance ofapproximately 5Ω due to these parasitic impedances. These parasiticimpedances may cause a positive shift in parasitic real resistance asthe parasitic reactance increases. Accordingly, the present applicationcontemplates offsetting the parasitic impedances (e.g., the realresistances and/or the imaginary reactances) presented by the testingequipment components to substantially reduce or eliminate the effect ofthose parasitic impedances on the wireless power transmitter 204 undertest. Example implementations may be described in more detail inconnection with FIGS. 4 and 5 below.

FIG. 4 shows a hybrid schematic/functional block diagram of an apparatus400 for testing an impedance range of a wireless power transmitter 204,in accordance with some exemplary implementations. The apparatus 400 maycomprise a loading test board configured to subject a wireless powertransmitter 204, under test (not shown in FIG. 4), to a range ofimpedances for determining whether the wireless power transmitter 204operates within desired parameters within that range of impedances. Insome implementations, the apparatus 400 may be used to test a chargingmat configured to simultaneously charge a number of different receiverdevices. As each receiver device may present a different impedance tothe transmit circuitry 206 in the mat based on its size, battery level,or other properties, it is desirable that the transmitter 204 within themat be able to operate efficiently over a large range of impedances.This test apparatus 400 may be used to simulate this range of loadimpedances to ensure proper operation.

The apparatus 400 may comprise an adjustable power supply 412electrically coupleable to, and configurable to drive, an adjustableimpedance circuit 440. In some implementations, in order to test thewireless power transmitter 204 (FIG. 2), for example, an output of thetransmit circuitry 206 may be connected as the adjustable power supply412, in lieu of the transmit coupler 214.

The adjustable impedance circuit 440 may comprise a first bank ofswitches 414, each switch connected in series with a first terminal ofthe power supply 412 and connected to a respective one of a plurality ofparallel-connected resistors in a first resistor bank 416. By closingone or more switches in the first bank of switches 414, correspondingresistors in the first resistor bank 416 may be switched into the pathof the power supply 412. The adjustable impedance circuit 440 mayadditionally comprise a second bank of switches 418, each switchconnected in series with the first resistor bank 416 and connected to arespective one of a plurality of parallel-connected capacitors in afirst capacitor bank 420. By closing one or more switches in the secondbank of switches 418, corresponding capacitors in the first capacitorbank 420 may be switched into the path of the power supply 412. Theadjustable impedance circuit 440 may additionally comprise a third bankof switches 422, each switch connected in series with the firstcapacitor bank 420 and connected to a respective one of a plurality ofparallel-connected inductors in a first inductor bank 424. By closingone or more switches in the third bank of switches 422, correspondinginductors in the first inductor bank 424 may be switched into the pathof the power supply 412.

The adjustable impedance circuit 440 may further comprise a fourth bankof switches 438, each switch connected in series with a second terminalof the power supply 412 and connected to a respective one of a pluralityof parallel-connected resistors in a second resistor bank 436. Byclosing one or more switches in the fourth bank of switches 438,corresponding resistors in the second resistor bank 436 may be switchedinto the path of the power supply 412. The adjustable impedance circuit440 may additionally comprise a fifth bank of switches 434, each switchconnected in series with the second resistor bank 436 and connected to arespective one of a plurality of parallel-connected capacitors in asecond capacitor bank 432. By closing one or more switches in the fifthbank of switches 434, corresponding capacitors in the second capacitorbank 432 may be switched into the path of the power supply 412. Theadjustable impedance circuit 440 may additionally comprise a sixth bankof switches 430, each switch connected in series with the secondcapacitor bank 432 and connected to a respective one of a plurality ofparallel-connected inductors in a second inductor bank 428. By closingone or more switches in the sixth bank of switches 430, correspondinginductors in the second inductor bank 428 may be switched into the pathof the power supply 412. By adjusting the switches in one or more of thefirst through sixth banks of switches 414, 418, 422, 438, 434, and 430,respectively, a range of impedances may be provided to a wireless powertransmitter 204 under test (not shown). Although a particulararrangement of components (e.g., parallel-connected components) is shownin the adjustable impedance circuit 440, the present application is notso limited, and the adjustable impedance circuit 440 may have anyarrangement (e.g., series connection, series-parallel connection, Piand/or delta connections, the use of variable impedance components, orany combination thereof) such that each of a resistance, capacitance,and inductance may be independently tuned or adjusted.

However, parasitic impedances in the adjustable impedance circuit 440(e.g., resistance and/or reactance of one or more of the resistors,capacitors, inductors or switches in the adjustable impedance circuit440) may prevent the adjustable impedance circuit 440 from achievingvery low impedances (e.g., approximately 1 ohm). In accordance with someimplementations, in order to minimize, substantially eliminate, orcompensate for these parasitic impedances, a transformer 426 is placedin series with, and at a balance point of, the adjustable impedancecircuit 440. The transformer 426 is configured to apply a voltage equalto a voltage drop caused by the parasitic impedances (e.g., the realresistance of the parasitic impedances) in series with the adjustableimpedance circuit 440. The balance point may be defined as a node withinthe adjustable impedance circuit 440 where a node voltage issubstantially half of a voltage across the power supply 412 at anyparticular time (e.g., where a substantially equal impedance is locatedbetween the first terminal of the power supply 412 and the balance pointand between the balance point and the second terminal of the powersupply 412. As shown in FIG. 4, this may be a point in the adjustableimpedance circuit 440 between the first and second inductor banks 424,428, although the balance point may be at another location depending onthe particular layout or design of the adjustable impedance circuit 440.

In FIG. 4, this parasitic impedance (e.g., real resistance) isdetermined, detected or measured utilizing a differential amplifier 402having first and second terminals connected to the adjustable impedancecircuit 440 before the first capacitor bank 420 and after the secondcapacitor bank 432, at nodes 442 and 444, respectively. The differentialamplifier 402 measures a voltage drop across the predominantly reactivecomponents of the adjustable impedance circuit 440 (e.g., the first andsecond capacitor banks 420, 432, the first and second inductor banks424, 428, and the associated banks of switches 418, 422, 430, 438) andutilizes this measurement to determine the actual parasitic impedancewhen no voltage is impressed across the transformer 426, and the neteffective parasitic impedance still remaining (e.g., to be attenuated orcanceled) when a voltage is injected by the transformer 426 during finetuning of the applied voltage.

In order to substantially cancel out the voltage drop caused by theparasitic impedance (e.g., the real resistance) of the predominantlyreactive components of the adjustable impedance circuit 440, the voltageapplied at the secondary coil (S) of the transformer 426 should havesubstantially the same magnitude as, and be substantially 180° out ofphase with, the voltage measured across the differential amplifier 402when no voltage is applied at the transformer 426 during loading. Inthis way, a root mean square (RMS) voltage drop of substantially zeromay be achieved across the differential amplifier's 402 inputs, and soat the output of the differential amplifier 402, due to the parasiticresistances of the predominantly reactive components of the adjustableimpedance circuit 440. Since there is substantially no effective RMSvoltage drop across the predominantly reactive components it thiscondition, a wireless power transmitter 204 under test will besubstantially unaffected by the actual parasitic resistances of thepredominantly reactive components of the adjustable impedance circuit440. Thus, the transformer 426 essentially applies, adds or presents anegative impedance (e.g., a negative real resistance) having a magnitudeequal to the magnitude of the parasitic impedance (e.g., the realresistance) of the predominantly reactive components to the adjustableimpedance circuit 440 during loading. In this way, the output of thedifferential amplifier 402 provides a feedback signal whose amplitude isproportional to the portion of the parasitic resistance of thepredominantly reactive components of the adjustable impedance circuit440 that has not been compensated for, or canceled out by, the addednegative resistance at the transformer 426.

To ensure the phase shift is correctly tuned to achieve the above-statedoutcome, the output of the differential amplifier 402 may be fed into aphase shift circuit 404. The phase shift circuit 404 is configured toadjust a phase of an output of the phase shift circuit 404 based on theoutput of the differential amplifier 402 (e.g., the phase is shifteduntil the output of the differential amplifier 402 has an amplitude ofsubstantially zero). The phase adjusted output of the phase shiftcircuit 404 may be input to a first driver circuit 406 a and to aninverter 408. The output of the inverter 408 may be fed into a seconddriver circuit 406 b. The outputs of the first driver circuit 406 a andthe second driver circuit 406 b form a differential drive amplifierconfigured to drive a voltage at the primary (P) coil of the transformer426. In some implementations, the phase shift circuit 404 may beconfigured to adjust the phase of its output signal until the amplitudeof the output of the differential amplifier 402 is substantially zero.This is because the voltage drop across the predominantly reactivecomponents of the adjustable impedance circuit 440 (and so across theinputs of the differential amplifier 402) will be substantially zerowhen the voltage induced in the secondary (S) coil of the transformer426 is equal in magnitude and 180° out of phase with the actual voltagedrop across the reactive components caused by the parasitic impedancesof the same. This may also be considered as when the negative resistanceapplied at the secondary coil of the transformer 426 has a substantiallyequal magnitude to that of the parasitic resistance of the substantiallyreactive components of the adjustable impedance circuit 440. In someother implementations, a differential driver amplifier setup may not beutilized. In these implementations, the first and second driver circuits406 a, 406 b and the inverter 408 may be replaced with a single drivercircuit (not shown) having its output terminals connected across theprimary coil of the transformer 426.

FIG. 5 shows another functional block diagram of an apparatus 500 fortesting an impedance range of a wirelessly power transmitter 204, inaccordance with some other exemplary implementations. FIG. 5 may be amore general implementation of the concepts previously described inconnection with FIG. 4. Thus, one or more components of the apparatus500 in FIG. 5 may correspond to, or may substitute for, one or morecomponents of the apparatus 400 in FIG. 4. In FIG. 5, the apparatus 500comprises a current sense transformer 502, which may correspond to, orperform a similar function as, the differential amplifier 402 of FIG. 4.Instead of measuring a voltage drop across the adjustable impedancecircuit 440 of FIG. 4, the current sense transformer 502 may beconfigured to sense a current proportional to a current passing throughan adjustable impedance circuit (not shown but analogous to the circuit440 of FIG. 4). Of course, the current sense transformer 502 may bereplaced with any other module or circuit configured to sense thecurrent circulating through, or the voltage appearing across at least aportion of the adjustable impedance circuit (not shown). The apparatus500 further comprises a unity gain buffer 504 accepting the output ofthe current sense transformer 502 as an input. The unity gain buffer 504provides impedance isolation between the current sense transformer 502and the components that follow the unity gain buffer 504.

The apparatus 500 additionally comprises an RLC passive circuit 506,which may be configured to receive the output of the unity gain buffer504 as an input and output a signal to each of a sine wave modulator 508and a cosine wave modulator 514. The sine wave modulator 508 isconfigured to multiply the output of the RLC passive circuit 506 with asine wave signal to output a modulated “in-phase” signal. Similarly, thecosine wave modulator 514 may be configured to multiply the output ofthe RLC passive circuit 506 with a cosine wave signal (e.g., aquadrature signal being 90° phase-shifted from the sine wave) to producea modulated “quadrature-phase” signal. In some implementations, theoutput of the sine wave modulator 508 may be an analog signal that isproportional to or corresponds with a real resistance of at least thepredominantly reactive components of the adjustable impedance circuit(not shown) of the apparatus 500. Likewise, the output of the cosinewave modulator 514 may be an analog signal that is proportional to orcorresponds with an imaginary resistance (i.e., reactance) of at leastthe predominantly reactive components of the adjustable impedancecircuit (not shown) of the apparatus 500. The apparatus 500 furthercomprises a first variable gain buffer 510 accepting the output of thesine wave modulator 508 as an input. The apparatus 500 further comprisesa second variable gain buffer 516 accepting the output of the cosinewave modulator 514 as an input. The first and second variable gainbuffers 510, 516 are configured to multiply their inputs byindependently adjustable amplification factors and provide themultiplied inputs as outputs to first and second multiplyingdigital-to-analog converters (DACs) 512, 518. The first multiplying DAC512 is configured to multiply a first input from the first variable gainbuffer 510 with a real resistance adjustment control signal from aprocessor 526 and output a modulated “in-phase” signal. Likewise, thesecond multiplying DAC 518 is configured to multiply a first input fromthe second variable gain buffer 516 with a reactance adjustment controlsignal from the processor 526 and output a modulated “quadrature-phase”signal.

The processor 526 is configured to receive signals indicating actualdetermined or measured resistance and reactance values of the adjustableimpedance circuit (not shown) of the apparatus 500 based on the currentsensed by the current sense transformer 502. The processor 526determines or calculates the appropriate values for the real resistanceadjustment control signal and the reactance adjustment control signalrequired to reduce or eliminate the net or effective parasiticresistance of the predominantly reactive components of the adjustableimpedance circuit (not shown) of the apparatus 500. The outputs of thefirst and second multiplying DACs 512, 518 (adjusted in-phase andquadrature-phase signals) are summed at a summing circuit 520, whichoutputs the summed signal to a power amplifier driver circuit 522. Insome implementations, one or more of the RLC passive circuit 506, sinewave modulator 508, cosine wave modulator 514, first and second variablegain buffers 510, 516, first and second multiplying DACs 512, 518,processor 526 and summing circuit 520 may correspond to the phase shiftcircuit 404 of FIG. 4. For example, by adjusting the real resistanceadjustment control signal and the reactance adjustment control signal,the magnitudes of the adjusted in-phase and quadrature-phase signals aremodified such that, when summed at the summing circuit 520, the summedoutput signal is analogous to or substantially proportional to aphase-shifted and/or amplitude-adjusted version of the unity gain buffer504 output (and so proportional to a phase-shifted (e.g., phasereversed) version of the current sensed by the current sense transformer502).

The power amplifier driver circuit 522 receives the output from thesumming circuit 520 and outputs a drive signal to a tuning transformer524. The tuning transformer 524 may correspond to, and may be similarlyconnected to the adjustable impedance circuit (not shown) as, thetransformer 426 of FIG. 4. In some implementations, the power amplifierdriver circuit 522 may correspond to the first and second drivercircuits 406 a, 406 b and the inverter 408 of FIG. 4.

The tuning transformer 524 may be configured to apply a voltage and/orcurrent proportional to the voltage and/or current, respectively, of thedrive signal input to the tuning transformer 524 back into theadjustable impedance circuit (not shown) of the apparatus 500 in orderto substantially cancel out the actual parasitic impedance of thepredominantly reactive components of the adjustable impedance circuit(not shown). In this way, the, net or effective parasitic impedance(e.g., resistance) of the adjustable impedance circuit (not shown) maybe maintained at a substantially zero value and the above-describeddifficulties of providing very low impedances (e.g., <1Ω) to a wirelesspower transmitter under test may be overcome.

FIG. 6 is a flowchart 600 depicting a method for testing an impedancerange of a wireless power transmitter, in accordance with some exemplaryimplementations. The flowchart 600 is described herein with reference toFIGS. 4 and 5. In an implementation, one or more of the blocks inflowchart 600 may be performed by a wireless power transmitter testingunit, such as the apparatus 400 or the apparatus 500 as shown in FIGS. 4and 5, respectively. Although the flowchart 600 is described herein withreference to a particular order, in various implementations, blocksherein may be performed in a different order, or omitted, and additionalblocks may be added.

At block 602, a parameter indicative of a parasitic impedance of anadjustable impedance circuit configurable to be connected to a powersource is sensed. For example, as previously described in connectionwith FIG. 4, the differential amplifier 402 may sense a voltage dropacross at least a portion of the adjustable impedance circuit 440 (e.g.,across the predominantly reactive components of the adjustable impedancecircuit 440). In other implementations, as previously described inconnection with FIG. 5, the current sense transformer 502 may sense acurrent proportional to the current passing through the adjustableimpedance circuit (not shown in FIG. 5).

At block 604, a transformer coupled to the adjustable impedance circuitis driven with a signal based on the sensed parameter that causes thetransformer to apply a first voltage to the adjustable impedancecircuit. The first voltage has a substantially same amplitude as avoltage drop caused by the parasitic impedance and is out of phase withthe voltage drop. For example, as previously described in connectionwith FIG. 4, the driver circuits 406 a, 406 b may drive a signal to theprimary (P) coil of the transformer 426, coupled to the adjustableimpedance circuit 440, based on the voltage drop measured by thedifferential amplifier 402 (e.g., the sensed parameter). Applying thesignal to the primary coil (P) of the transformer 426 may cause thesecondary coil (S) of the transformer to apply a first voltage to theadjustable impedance circuit 440 having a substantially same amplitudeas the sensed voltage drop and being 180° out of phase with the sensedvoltage drop. In some other implementations, as previously described inconnection with FIG. 5, the driver circuit 522 may apply a signal to thetuning transformer 524 based on the current sensed by the current sensetransformer 502 that causes the tuning transformer 524 to apply a firstvoltage into the adjustable impedance circuit 440 having a substantiallysame amplitude as a voltage drop across the predominantly reactivecomponents of the adjustable impedance circuit and being 180° out ofphase with that voltage drop.

FIG. 7 is a functional block diagram of an apparatus 700 for testing animpedance range of a wireless power transmitter, in accordance with someexemplary implementations. The apparatus 700 may be configured toperform one or more operations as previously described in connectionwith FIG. 6. The apparatus 700 includes means 702 for providing anadjustable impedance to a power source. In some implementations, themeans 702 may comprise the adjustable impedance circuit 440 of FIG. 4,or the adjustable impedance circuit (not shown) as previously describedin connection with FIG. 5.

The apparatus 700 further includes means 704 for sensing a parameterindicative of a parasitic impedance of the means for providing theadjustable impedance. In some implementations, the means 704 may beconfigured to perform the operation of operation block 602 previouslydescribed in connection with FIG. 6. In some implementations, means 704may comprise the differential amplifier 402 of FIG. 4, or alternatively,the current sense transformer 502 of FIG. 5.

The apparatus 700 further includes means 706 for means for applying afirst voltage to the means 702 for providing the adjustable impedancebased on the sensed parameter. The first voltage has a substantiallysame amplitude as a voltage drop caused by the parasitic impedance. Thefirst voltage is out of phase with the voltage drop. In someimplementations, the means 706 may be configured to perform theoperation of operation block 604 previously described in connection withFIG. 6. In some implementations, means 706 may comprise one or more ofthe differential amplifier 402, the phase shift circuit 404, the drivercircuits 406 a, 406 b, the inverter 408, and the transformer 426, aspreviously described in connection with FIG. 4. In some otherimplementations, the means 706 may comprise one or more of the modules502-526, as previously described in connection with FIG. 5.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. The described functionality may be implemented in varying waysfor each particular application, but such implementation decisionsshould not be interpreted as causing a departure from the scope of theimplementations.

The various illustrative blocks, modules, and circuits described inconnection with the implementations disclosed herein may be implementedor performed with a general purpose processor, a Digital SignalProcessor (DSP), an Application Specific Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm and functions described in connectionwith the implementations disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. If implemented in software, the functions may bestored on or transmitted over as one or more instructions or code on atangible, non-transitory computer-readable medium. A software module mayreside in Random Access Memory (RAM), flash memory, Read Only Memory(ROM), Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, a CDROM, or any other form of storage medium known in the art. A storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Diskand disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and Blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer readable media. The processor andthe storage medium may reside in an ASIC.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features have been described herein. It is to be understoodthat not necessarily all such advantages may be achieved in accordancewith any particular implementation. Thus, one or more implementationsachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

Various modifications of the above described implementations will bereadily apparent, and the generic principles defined herein may beapplied to other implementations without departing from the spirit orscope of the application. Thus, the present application is not intendedto be limited to the implementations shown herein but is to be accordedthe widest scope consistent with the principles and novel featuresdisclosed herein.

What is claimed is:
 1. An apparatus for testing an impedance range of awireless power transmitter, comprising: an adjustable impedance circuitconfigurable to be connected to a power source; a transformer coupled tothe adjustable impedance circuit; a sensing circuit configured to sensea parameter indicative of a parasitic impedance of the adjustableimpedance circuit; and a driver circuit configured to drive thetransformer with a signal based on the sensed parameter that causes thetransformer to apply a first voltage to the adjustable impedancecircuit, the first voltage having a substantially same amplitude as avoltage drop caused by the parasitic impedance and being out of phasewith the voltage drop.
 2. The apparatus of claim 1, wherein the sensedparameter is at least one of a current circulating in the adjustableimpedance circuit or a voltage across at least a portion of theadjustable impedance circuit.
 3. The apparatus of claim 1, wherein theparasitic impedance has a parasitic resistance, and wherein thetransformer is configured to add a negative resistance to the adjustableimpedance circuit by applying the first voltage to the adjustableimpedance circuit, the negative resistance being substantially equal inmagnitude to the parasitic resistance.
 4. The apparatus of claim 1,wherein the transformer is coupled to a balance point of the adjustableimpedance circuit.
 5. The apparatus of claim 4, wherein the balancepoint comprises a node within the adjustable impedance circuit where anode voltage is substantially half of a voltage across the power source.6. The apparatus of claim 1, further comprising a phase-shift circuitconfigured to shift a phase of the sensed parameter and provide thephase-shifted sensed parameter to the driver circuit.
 7. The apparatusof claim 6, wherein the phase-shift circuit is configured to shift thephase of the sensed parameter until the first voltage injected into theadjustable impedance circuit is 180° out of phase with the voltage drop.8. The apparatus of claim 1, wherein the sensing circuit comprises atleast one of a current sense transformer or a differential amplifier. 9.The apparatus of claim 1, wherein the adjustable impedance circuit isconfigurable to present an adjustable impedance to a wireless powertransmit circuit of the wireless power transmitter.
 10. A method fortesting an impedance range of a wireless power transmitter, comprising:sensing a parameter indicative of a parasitic impedance of an adjustableimpedance circuit configurable to be connected to a power source, anddriving a transformer coupled to the adjustable impedance circuit with asignal based on the sensed parameter that causes the transformer toapply a first voltage to the adjustable impedance circuit, the firstvoltage having a substantially same amplitude as a voltage drop causedby the parasitic impedance and being out of phase with the voltage drop.11. The method of claim 10, wherein the sensed parameter is at least oneof a current circulating in the adjustable impedance circuit or avoltage across at least a portion of the adjustable impedance circuit.12. The method of claim 10, wherein the parasitic impedance has aparasitic resistance and the method further comprises providing anegative resistance to the adjustable impedance circuit by applying thefirst voltage to the adjustable impedance circuit, the negativeresistance being substantially equal in magnitude to the parasiticresistance.
 13. The method of claim 12, wherein the first voltage isapplied to a balance point of the adjustable impedance circuit, thebalance point having node voltage that is substantially half of avoltage across the power source.
 14. The method of claim 10, furthercomprising shifting a phase of the sensed parameter and providing thephase-shifted sensed parameter to a driver circuit for driving thetransformer.
 15. The method of claim 14, further comprising shifting thephase of the sensed parameter until the first voltage applied to theadjustable impedance circuit is 180° out of phase with the voltage drop.16. The method of claim 10, further comprising presenting an adjustableimpedance to a wireless power transmit circuit of the wireless powertransmitter.
 17. An apparatus for testing an impedance range of awireless power transmitter, comprising: means for providing anadjustable impedance to a power source; means for sensing a parameterindicative of a parasitic impedance of the means for providing theadjustable impedance; and means for applying a first voltage to themeans for providing the adjustable impedance based on the sensedparameter, the first voltage having a substantially same amplitude as avoltage drop caused by the parasitic impedance and being out of phasewith the voltage drop.
 18. The apparatus of claim 17, wherein theparasitic impedance has a parasitic resistance, the apparatus furthercomprising means for adding a negative resistance to the means forproviding the adjustable impedance by applying the first voltage to themeans for providing the adjustable impedance, the negative resistancebeing substantially equal in magnitude to the parasitic resistance. 19.The apparatus of claim 17, further comprising means for shifting a phaseof the sensed parameter and providing the phase-shifted sensed parameterto the means for applying the first voltage to the means for providingthe adjustable impedance.
 20. The apparatus of claim 19, wherein themeans for shifting the phase of the sensed parameter is configured toshift the phase of the sensed parameter until the first voltage is 180°out of phase with the voltage drop.